The present invention pertains to a process for manufacturing a catalyst support based on practically dehydroxylated silica and anhydrous magnesium chloride, the resultant support, and ethylene and alpha-olefin polymerization and copolymerization catalysts based on this support.
It is known that silica can be used as a catalyst support and particularly as a support for the polymerization and copolymerization of alpha-olefins. These catalysts, in general, are constituted of an active product based on magnesium chloride, a halide of a transition metal from Groups IV, V and VI of the Periodic Table of the Elements, preferably titanium, possibly an electron donor and/or an organometallic compound of a metal from Group III of the Periodic Table of the Elements, preferably aluminum.
Before its use as a catalyst support, the silica is usually dehydroxylated by a heat treatment at a high temperature generally above 600.degree. C. In this case the structure of the silica may be transformed and its properties as a catalyst support may become very mediocre. At any rate, there remains a hydroxyl level much higher than 100 micromoles per gram of silica at temperatures at which the porous texture collapses. This is why the hydroxyl groups of the silica are practically preserved for this application. However, these hydroxyl groups may be harmful for the activity of the support-type catalyst. This happens, e.g., in the case of TiCl.sub.4, which is susceptible to reaction with the hydroxyl groups of the silica to form Si--O--TiCl.sub.3 and Si--O--TiCl.sub.2 -type bonds, and the activity of the titanium decreases in this form during the polymerization.